The person who was just there at the top of the stairs? They're going to be your boss.
The person just now at the top of the stairs will become your boss.
人 = The person
ちょうど今 = (who) was just (now)
上にいる = (there) at the top
あの階段 = of the stairs
になる = will become
あなたの上司 = your boss.
強調するために、ほとんどのネイティブスピーカーは最初の部分を最後の部分と分かれ、質問をします。
"You see that person there? That's the principal of the school." 「あそこにいるひとは校長ですよ。」
日本 
アメリカ合衆国 
